This invention relates generally to seals and, more particularly, to radial seals for sealing a cylindrical surface of a movable member.
Many types of seal configurations have been employed for sealing rotating or reciprocating cylinders or shafts. Each type of seal configuration is adapted to perform well under certain operating conditions, but is less well suited for other conditions.
For instance, lip type seals are particularly well suited for dynamic applications. In a dynamic application, the lip of the seal slides either axially or rotationally upon the surface being sealed.
Another type of dynamic seal, disclosed in U.S. Pat. No. 4,151,999, issued to Ringel et al. on May 1, 1979 and assigned to the assignee hereof, has an inner nylon seal ring which provides dynamic sealing capability against a rotating shaft in a non-lubricated environment.
In applications where only a small amount of movement is all that ever occurs, a shear-type seal may be employed. U.S. Pat. No. 3,158,923, issued Dec. 1, 1964 to Reinsma and also assigned to the assignee hereof, shows a typical shear-type seal employed in a track joint assembly. A track joint has only limited angular movement which is accommodated through flexure of an elastic ring seal member.
However, in some applications, seals must contend with both dynamic and small movement conditions. The recoil cylinder for a track recoil mechanism of a track-type vehicle is such an application. In addition, such seal is exposed to adverse environmental conditions. The recoil cylinder seal must not only seal lubricant within the recoil mechanism, it must also seal out highly abrasive materials, such as sand and mud, and be able to seal out those materials after they have become dried and caked or after being frozen about the cylinder. As a consequence, such seal must be extremely abrasion resistant and tough so as to withstand such adverse conditions.
Upon recoil, the recoil cylinder moves axially a distance frequently in excess of 50 millimeters. This movement is referred to herein as extended travel-type movement. This extent of movement requires dynamic sealing capability of the seal. Recoil movements occur only when the track hits an obstruction or when an object, such as a rock, becomes temporarily lodged in the track. Such occurrences happen relatively infrequently.
In addition to the above recoil movements, it has been found that the recoil cylinder also experiences a high number of much smaller movements, referred to herein as dither-type movements. It has been found that these dither-type movements are principally caused by the repetitious impacting of the track links against the idler wheel as the track travels about the idler during vehicle operation. These dither movements can be radial, orbital, and axial.
With the use of a conventional dynamic seal, these dither movements cause rapid, deleterious wear of the seal. Even more serious is the damage caused to the cylinder itself. The small, repetitious movements between the seal and the cylinder at one localized area on the cylinder in the presence of abrasives causes a groove to be cut into the cylinder under the seal. This undue wear and damage results in loss of sealing and also necessitates the premature replacement of both the seal and cylinder, resulting in undue waste and downtime for the vehicle.
The present invention is directed to overcome one or more of the problems as set forth above.